1. Field of the Invention
This invention relates to a light emitting diode module, more particularly to a light emitting diode modulo including light emitting diodes having stepped sides, and a method of making the same.
2. Description of the Related Art
Referring to FIG. 1, a conventional light emitting diode (LED) module 1 includes a substrate 11, and a plurality of LEDs 12 that are formed on the substrate 11 and that are arranged in an array. Since the LEDs 12 adjacent to each other are electrically interconnected in the same manner, only two of the LEDs 12 are shown in FIG. 1 for the sake of clarity.
Each of the LEDs 12 includes a light emitting unit 121, a p-electrode 122, and an n-electrode 123. The p-electrode 122 and the n-electrode 123 are formed on the light emitting unit 221. Confronting lateral sides 124 of the adjacent pair of the light emitting units 121 and a portion of a top surface 111 of the substrate 11 cooperatively define a groove 120. An insulating layer 13 is formed in the groove 120 and on a portion of each of the light emitting units 121. The insulating layer 13 is in contact with the n-electrode 123 on one of the light emitting units 121 and the p-electrode 122 on the other one of the light emitting units 121. An electrically conductive layer 14 is formed on the insulating layer 13 so that two ends thereof are in contact with the n-electrode 123 on one of the light emitting units 121 and the p-electrode 122 on the other one of the light emitting units 121 to establish an electrical connection.
The insulating layer 13 is formed by virtue of a spin-on-glass (SOG) coating process. Specifically, the groove 120 is filled with a liquid solution containing a dielectric material (e.g., SiO2) using a spin-coating process, and the aforementioned liquid solution is also disposed on the portion of each of the adjacent pair of the light emitting units 121 via the spin coating process. Subsequently, a heating process is conducted so as to evaporate a solvent in the aforementioned liquid solution. Consequently, the remaining solidified dielectric material forms the insulating layer 13.
Each of the confronting lateral sides 129 of the light emitting units 121 extends upwardly from the substrate 11, and thus has a relatively high vertical face. Uniformly coating the dielectric material on the relatively high vertical faces of the lateral sides 124 is difficult. Referring to FIG. 2, if an insulating layer 13′ is formed on the confronting lateral sides 124 as a thin film, the insulating layer 13′ will be non-uniform at the vertically extending portions thereof. Likewise, if an electrically conductive layer 14′ is formed on the insulating layer 13′, a uniform vertical conductive layer will be hardly formed on the relatively high vertical faces of the confronting lateral sides 124. The non-uniform electrically conductive layer 14′ may break even when a small current is applied to the LED module 1.
Accordingly, the groove 120 has to be filled with the insulating layer 13 as shown in FIG. 1 to reduce the length of the vertically extending portion of the electrically conductive layer 19 to be formed on the insulating layer 13. The insulating layer 13 filled in the groove 120 has a thickness of about several micrometers. When the insulating layer 13 is made from SiO2, the insulating layer 13 which fills the groove 120 has a transmittance substantially as low as 25% to 45% for light having a wavelength of 455 nm, thereby reducing the rate of lateral emission of light and hence light emitting efficiency of LED module 1.
In addition, vacuum deposition processes (e.g., sputtering, evaporation, etc.) are not suitable to form the insulating layer 13 shown in FIG. 1 since the vacuum deposition processes require longer time to form a film having a thickness of several micrometers compared to the spin-coating process. Although the spin-coating process provides a fast rate of forming a film, the thickness of the film can not be controlled precisely. A chemical mechanical polishing (CMP) process is necessary to polish an uneven surface of a thick film made using the spin-coating process. However, equipment for the CMP process is costly and may therefore increase a production cost of the LED module 1.